Back to Lymphocytes

Thymocytes which originate in the thymus give rise to T-lymphocytes. Large numbers of small lymphocytes are also found in the kidney and spleen and it is thought that circulating lymphocytes are of two types:  T-cells of thymic origin, and B-cells which are believed to originate in the kidney.

Definitions

THYMUS: A paired lymphoid gland situated dorso-laterally in the gill chamber.  The site of T-lymphocyte production, it is regulated by hormones produced by thymic epithelial cells. In fish (and in all vertebrates) the thymus gradually atrophies after the onset of sexual maturity but does not completely disappear.

KIDNEY: Organ of excretion and water regulation in vertebrates, consisting of numerous nephrons and their blood supply.   The kidney also functions in formation of blood cells in some animals including the bony fishes.

SPLEEN: Organ comprising a mass of lymphoid tissue in the mesentery; unlike lymph nodes it is interposed in the blood circulation.